Electric circuits



y 7 1950 J. STIVIN 2,507,282

ELECTRIC CIRCUITS Filed Jan. 25, 1947 122/21 elz bol Ji kz v 012/Patented May 9, 1950 ELECTRIC CIRCUITS Jii'i Stivin, Celakovice, nearPrague, Czechoslovakia Application January 23, 1947, Serial No. 723,795In Germany November 24, 1942 1 Claim.

In the arrangements, in which the electron tube functions as oscillatororamplifier, the magnitude of the output delivered depends, among otherfactors, also on the emission current of the cathode. If the electrontube should already operate in the saturated region of thecharacteristic, it is not possible to obtain a higher emission current.Although, by overheating the cathode this can be achieved, it will be atthe cost of shortening the life of the cathode.

When operating only for a short time and intermittently, in thearrangements as hitherto used the electron tube is mostly heatedcontinuously to a heating voltage, at which the cathode delivers theemission current required during operation. The result of this is, thatthe time, during which the electron tube can be kept in use, amounts toonly a small fraction of the actual life of the cathode.

It is not possible to switch the heating on to the electron tube only atthe moment, in which a high voltage is applied to the anode, as it takesa certain amount of time to heat up the cathode and, with the majorityof the larger electron tubes, cannot be done intermittently andsuddenly. In those cases, in which it is a question of a periodic andrapidly recurring initiation of a temporary mode of operation of thearrangement, as, for instance, with oscillators for metallurgicalpurposes, a rapid heating up and extinction of the cathode would resultin its early destruction.

In order to make an intermittent heating of the filament possible, thefilament resistance would have to be made so great that the switching incurrent does not exceed a certain maximum value. Now, for this purposeit is proposed according to the invention to heat the filament to atemperature, at which the filament resistance already reaches a valuewhich prevents the occurrence of dangerous currents. This resistance isreached at a considerably lower temperature than the normal temperatureof the filament. Consequently, the vaporisation of the filament materialis less great in these intermediate periods and therefore the life ofthe filament correspondingly greater. On the other hand, it becomespossible to overheat the cathode during short working periods, withoutreducing its total life, as an increased filament vaporisation lastingonly a short time during the working periods is compensated by a reducedvaporisation during the inoperative periods. It is clear, that thisarrangement will have all the more importance, the shorter the operativeperiods and the longer the inoperative periods.

In its practical embodiment the whole arrangement will be somewhat asfollows. The electron tube is heated to a, lower voltage than when inoperation, for instance to of the working voltage, whereby the filamentvaporisa tion is kept down to about 50%. At the com-i mencement of theworking period the cathode is overheated intermittently to a highervoltage than the normal working voltage, for instance to of the latter,whereby the filament vaporisation and the emission current are increasedby about 50%. If the duration of the operative period to that of theinoperative period be, say, 1:1, there will be no shortening of the lifeand the output delivered will be about 50% higher.

To take another case, the electron tube is heated to, say, only 80% ofthe normal heating voltage and is thereupon additionally heated duringthe operation up to the full normal heating voltage. In this case therewill be no increase in the delivered output, but the life of theelectron tube is increased in accordance with the ratio of the operativeperiod to the inoperative period.

The ratio of the underheating to the overheating of the filament can ofcourse be optionally adjusted according to the desired life and theoutput to suit given operative conditions.

In the accompanying drawing an example is shown of the diagram ofconnections of an arrangement for carrying the mode of operationaccording to the invention into effect.

This arrangement consists substantially of two switching devices I, 2,one of which, I, closes the circuit, by means of which the electron tube3 has the lower anode voltage applied to it, whilst the other, 2, thenenables the actual, either normal or increased operative anode voltageto be applied. The first switching device I is built into current leadof a three-phase current generator and is actuated by means of asolenoid 4. The circuit closed thereby leads, for instance, throughresistances 5 to the rectifier 6 feeding the anode of the electron tube3.

The cathode of this electron tube 3 is heated by the secondary currentof the transformer l, the primary side of which is fed by one phase ofthe three-phase generator. In the primary side of this transformer thereis also a resistance 8. By these two resistances, 5 and 8, the circuitis kept at the low voltage, even during the inoperative periods. Whenthis voltage is to be raised to the useful operative voltage, the tworesistances are short-circuited.

For this purpose there is provided at the resistances 5 the switchingdevice 2 which is built into bridging leads and is in this case againactuated by a solenoid 9, whilst the short-circuiting of the resistance8 is effected by a switch l by means of the solenoid I I. Theresistances 5, S can, of course, be replaced by inductances orself-acting inductions, such as autotransformers, choking coils and thelike.

For facilitating the operation and manipulation of the whole arrangementspecial pressbutton switches I2, [3 are provided, by means of which thetwo switching devices I, 2 are, on the one hand, operated and, on theother hand, held in the operative position as long as desired. On thestarting button of the double switch l2 being depressed, the solenoid 4of the switching device I is energized and, similarly, on the startingbutton of the double switch l3 being depressed, the correspondingsolenoid 9 of the switching device 2 is energized. For holding the twoswitching devices in their operative position, there is connected toeach of them a further switch stage, I4 and i5 respectively, which, whenthe circuits of the respective solenoids have once been connected up,keeps them closed. For interrupting these holding circuits, each of thedouble switches, l2 and I3, is provided with a circuitbreaking button.

I claim:

In a thermionic vacuum tube oscillator circuit for high frequencyheating in metallurgical apparatus wherein the heated vacuum tubes aresubject only to intermittent loads, conductors forming a supply circuitfor the plate of each vacuum tube, resistances in the conductors formingthe plate supply circuit for varying the plate to cathode voltage, ashunt circuit around each resistance, a relay having a pair of contactsin each shunt circuit, conductors forming a cathode supply circuitconnected to said plate supply circuit, an impedance connected in atleast one of said cathode supply conductors, a shunt circuit around saidlatter impedance, a second relay having its load contacts connected insaid latter shunt circuit, and a primary circuit for said latter relayincluding one pair of load contacts of the first relay.

JIRI' STIVI'N.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,729,091 Atherton Sept. 24, 19292,055,921 Baker Sept. 29, 1936 2,103,334 McWeeny Dec. 28, 1937 2,211,985Peters Aug. 20, 1940 2,407,113 Tuck Sept. 3, 1946

